1. Using
FORCE

2. Using
FORCE

3. More mass = More inertia
Inertia review…
“The vis insita, or innate force of matter is a power of resisting, by which every body, as much as in it lies, endeavors to preserve in its present state, whether it be of rest, or of moving uniformly forward in a straight line.”
In English, please!
Inertia is the resistance of an object to a
change in its state of motion.
A bowling ball has more inertia than a soccer ball.
Don’t believe me?
Kick the bowling ball, then kick the soccer ball.
More mass = More inertia
More inertia
Less inertia

4. Force? Force has both direction and magnitude
A force is a push or pull upon an object resulting from the object's interaction with another object.
Forces only exist as a result of an interaction.
Force has both direction and magnitude

5. “A force is a push or pull upon an object”
When a force “pushes” on an object, it creates compression, a force that squeezes materials together.
When a force “pulls” on an object, it creates tension, a force that pulls materials apart.

6. I’ll leave it to you to be the judge of that…
“Why should I care about compression and tension?”
I’ll leave it to you to be the judge of that…

7. Balanced vs. Unbalanced forces
A soccer ball sits alone on the field, quiet and still…
Ground pushing up
Forces are balanced so ball does not move
Gravity pulling down

8. Balanced vs. Unbalanced forces
Suddenly….
An unbalanced force is exerted on the ball in the direction of the arrow, causing it to move in that direction until…

9. Balanced vs. Unbalanced forces
…its motion is stopped by an interaction with another force!
Once again, the forces are balanced and all is well in the universe.

10. If the forces acting on an object are balanced, the object is at rest.
Balanced Forces
If the forces acting on an object are balanced, the object is at rest.
We say the
“Net Force” = 0
Net force = sum of all forces acting on an object

11. Unbalanced Forces If the forces acting on an object become unbalanced,
the object moves in the direction of the greatest net force.
Force applied in this direction
In this case, the “Net Force” = 5 Newtons to the left

12. Mmmm, Newtons! kg ● m s2 1 N = 1 Oh, sorry, wrong Newtons
The newton is a unit of force that is defined as the amount of force required to accelerate a mass of one kilogram at a rate of one meter per second per second.
Algebraically:
1 N = 1
kg ● m s2

13. Diagramming Forces
If you were paying attention, you would have noticed that forces were illustrated using arrows. The size and direction of the arrow represents the relative strength and direction of the force.
Balance forces - arrows equal in length
Unbalanced forces - arrows not equal,
Movement is to the right

14. Diagramming Forces
If you were paying attention, you would have noticed that forces were illustrated using arrows. The size and direction of the arrow represents the relative strength and direction of the force.
Balance forces - arrows equal in length
Unbalanced forces - arrows not equal,
Movement is to the right

15. Calculating Net Forces
To calculate net forces, add all forces exerted on the object.
In this example, the net force up the ramp is greater than gravity, and the piano is moved forward and up the ramp into the truck. 1 2
For this example
Net force = (force 1 + force 2) + force 3 3

16. Calculating Net Forces1 2
For this example
Net force = force 1 - force 2
The force due to gravity in this example is negligible
What other forces can you identify in this picture?

17. The dogs exert a force on the toy as they bite down on it
Calculating Net Forces 1 2
The dogs exert a force on the toy as they bite down on it

18. Which ram seems to have the advantage?
Feeling the Force
Pow!
Which ram seems to have the advantage?
Why?

19. Newton’s First Law of Motion
“Every body perseveres in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed.”
Not again!
One more time…
English, please!
“An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.”
AKA - The Law of Inertia

20. Newton’s First Law of Motion
Said another way, Newton’s First Law of Motion states that a moving object moves in a straight line with constant speed unless a force acts on it.
 An object will not start moving unless a force acts on it
 An object will not stop moving unless a force acts on it
 An object will not change speed unless a force acts on it
 An object will not change direction unless a force acts on it

21. A force that opposes motion between two surfaces that are touching
Friction
A force that opposes motion between two surfaces that are touching
Even surfaces that seem to be extremely smooth have microscopic hills and valleys, and when two surfaces are in contact, the hills and valleys of one stick to the hills and valleys of the other, causing friction to resist the force of motion

22. The friction that exists between two objects in contact
Static friction
The friction that exists between two objects in contact

23. Friction Sliding friction
When force is applied that is strong enough to break the bonds of static friction and movement starts, sliding friction acts to slow that object down

24. Friction Rolling friction
The resistance that occurs when a round object such as a ball or tire rolls on a flat surface

25. Friction Fluid friction
Fluid friction occurs when a solid object travels through a liquid or gas.
Wake turbulence and wingtip vortices from jet airliner passing through a layer of clouds, showing the fluid nature of air

26. Force required to overcome friction
Increasing Force
Static friction
Sliding friction
Rolling friction
Fluid friction
Movement starts
Friction always acts in the opposite direction of movement, and always acts to slow object down.

27. Force and Newton’s Laws note-taking sheet
Section 1
Force
1. net
2. balanced
3. unbalanced
B. first law
C. Friction
1. slows down
2. Static
3. Sliding
4. Rolling

28. Newton’s Second Law of Motion
Force equals mass times acceleration (F = ma)
The net force on an object is equal to the mass (m) of the object multiplied by its acceleration (a)
Units of Force
Mass = kilograms (kg)
Acceleration = (m/s2)
Therefore….
F = kg ● m/s2
Force is measured in (Newtons, that is)

29. What are the forces acting on this bicycle and rider, coasting along at 25 km/h on this flat, wet, Alaskan road?

30. *Momentum = mass (kg) ● velocity (m/s)
A = force of gravity
B = force of the road (Normal
C = rolling frictional force
D = force of momentum*
E = fluid frictional force (air or wind resistance) A E D B C
*Momentum = mass (kg) ● velocity (m/s)

31. Is the net force balanced?
A = force of gravity
B = force of the road (Normal force)
C = rolling frictional force
D = force of momentum*
E = fluid frictional force (air or wind resistance) A
Is the net force balanced?
Write out the formula… E D B C
Net force = (A-B) + D - (E+C)

32. Calculating Net Force
When the forces are acting on an object from the same direction, you add
When the forces are acting on an object from different directions, you subtract

33. Calculating Net Force
When the forces are acting on an object from the same direction, you add
10 N
2 N (Normal Force)
2 N (Gravitational Force)
(2N – 2N) + (10 N + 10 N) = 20 N to the right
When the forces are acting on an object from different directions, you subtract
10 N
11 N
2 N (Normal Force)
2 N (Gravitational Force)
(2N – 2N) + (11 N - 10 N) = 1 N to the left

34. Can an object be in motion and the net force = 0?
Yes. Once an object is in motion, if no other forces such as friction are acting on it, the object will remain in motion in a straight line.
Point of clarification:
Forces do not cause motion
forces cause accelerations.

35. Today – complete worksheets on forces (trays 1-4)
Note – On the “Identifying Forces” worksheet, you will see some problems in which the vertical forces and horizontal forces are not balanced.
10 N
20 N
15 N
In these problems, solve for the net force and indicate direction. For example, using the diagram to the left you would have
(20 N – 10 N) + (15 N – 10 N) = 10 N up, 5 N right
Motion would be up and to the right

36. Look carefully at these illustrations
Look carefully at these illustrations. Decide which of Newton’s laws is illustrated in each example. Explain how the situation illustrates the law you chose. 1 2 3 4 5 6